The -fconserve-space flag has been
+ deprecated. The flag had no effect for most targets: only
+ targets without a global .bss section and without
+ support for switchable sections. Furthermore, the flag only
+ had an effect for G++, where it could result in wrong semantics
+ (please refer to the GCC manual for further details).
+ The flag will be removed in GCC 4.8
Support for a number of older systems and recently + unmaintained or untested target ports of GCC has been declared + obsolete in GCC 4.7. Unless there is activity to revive them, the + next release of GCC will have their sources permanently + removed.
+ +All GCC ports for the following processor + architectures have been declared obsolete:
+ +picochip-*)The following ports for individual systems on + particular architectures have been obsoleted:
+ +-munaligned-access is active by default, which for
+ some source codes generates code that accesses memory on unaligned
+ addresses. This will require the kernel of those systems to enable
+ such accesses (controlled by CP15 register c1, refer
+ to ARM documentation). Alternatively or for compatibility with
+ kernels where unaligned accesses are not supported, all code has
+ to be compiled with -mno-unaligned-access.
+ Linux/ARM in official releases has automatically and
+ unconditionally supported unaligned accesses as emitted by GCC due
+ to this option being active, since Linux version 2.6.28.The obsolete ports with alternatives are:
+ +Note, however, that these alternatives are not binary compatible + with their legacy counterparts (although some can support running legacy + applications).
+The obsolete ports that currently lack a modern alternative are:
+ +--enable-threads=solaris configure option and
+ the -threads compiler option don't work any longer./usr/ucbinclude and
+ /usr/ucblib. It has been removed from Solaris 11, and was
+ only intended as a migration aid from SunOS 4 to SunOS 5. The
+ -compat-bsd compiler option is not recognized any
+ longer.-mwords-little-endian option has
+ been deprecated. It will be removed in a future release."l"
+ constraint in MIPS16 asm statements.std::list changing its size and altering the definitions of
+ some member functions, and std::pair's move constructor was
+ non-trivial which altered the calling convention for functions with
+ std::pair arguments or return types. The ABI incompatibilities
+ have been fixed for GCC version 4.7.2 but as a result C++11 code compiled
+ with GCC 4.7.0 or 4.7.1 may be incompatible with C++11 code compiled with
+ different GCC versions and with C++98/C++03 code compiled with any version.
+ --param case-values-threshold=n
+ was added to allow users to control the cutoff between doing switch statements
+ as a series of if statements and using a jump table.
+ ld -r is now supported with LTO.
+void foo(int a)
+{
+ if (a > 10)
+ ... huge code ...
+}
+void bar (void)
+{
+ foo (0);
+}
+
+ The call of foo will be inlined into bar even when
+ optimizing for code size. Constructs based on __builtin_constant_p
+ are now understood by the inliner and code size estimates are evaluated a lot
+ more realistically.alias attribute) has been re-engineered. Aliases no
+ longer pose optimization barriers and calls to an alias can be inlined
+ and otherwise optimized.
+void foo(bool flag)
+{
+ if (flag)
+ ... do something ...
+ else
+ ... do something else ...
+}
+void bar (void)
+{
+ foo (false);
+ foo (true);
+ foo (false);
+ foo (true);
+ foo (false);
+ foo (true);
+}
+
+ GCC will now produce two copies of foo. One with flag being
+ true, while other with flag being
+ false. This leads to performance improvements previously
+ possible only by inlining all calls. Cloning causes a lot less code size
+ growth.strlen, strchr, strcpy,
+ strcat, stpcpy and their
+ _FORTIFY_SOURCE counterparts into faster alternatives.
+ This pass is enabled by default at -O2 or above, unless
+ optimizing for size, and can be disabled by the
+ -fno-optimize-strlen option. The pass can e.g. optimize
+
+char *bar (const char *a)
+{
+ size_t l = strlen (a) + 2;
+ char *p = malloc (l); if (p == NULL) return p;
+ strcpy (p, a); strcat (p, "/"); return p;
+}
+
+ into:
+
+char *bar (const char *a)
+{
+ size_t tmp = strlen (a);
+ char *p = malloc (tmp + 2); if (p == NULL) return p;
+ memcpy (p, a, tmp); memcpy (p + tmp, "/", 2); return p;
+}
+
+ or for hosted compilations where stpcpy is available in the
+ runtime and headers provide its prototype, e.g.
+
+void foo (char *a, const char *b, const char *c, const char *d)
+{
+ strcpy (a, b); strcat (a, c); strcat (a, d);
+}
+
+ can be optimized into:
+
+void foo (char *a, const char *b, const char *c, const char *d)
+{
+ strcpy (stpcpy (stpcpy (a, b), c), d);
+}
+
+ -feliminate-unused-debug-types
+ has been re-enabled by default, as it is for the other languages,
+ leading to a reduction in debug info size of 12.5% and more for
+ relevant cases, as well as to a small compilation speedup.__builtin_assume_aligned, has been added,
+ through which the compiler can be hinted about pointer alignment
+ and can use it to improve generated code.
+
+ Experimental support for transactional memory has been added.
+ It includes support in the compiler, as well as a supporting
+ runtime library called libitm. To compile code
+ with transactional memory constructs, use
+ the -fgnu-tm option.
+
+ Support is currently available for Alpha, ARM, PowerPC, SH, SPARC, + and 32-bit/64-bit x86 platforms. +
+ ++ For more details on transactional memory + see the GCC + WiKi. +
+
+ Support for atomic operations specifying the C++11/C11 memory model
+ has been added. These new __atomic routines replace the
+ existing __sync built-in routines.
+
+ Atomic support is also available for memory blocks. Lock-free + instructions will be used if a memory block is the same size and + alignment as a supported integer type. Atomic operations which do not + have lock-free support are left as function calls. A set of library + functions is available on the GCC atomic wiki in the "External + Atomics Library" section. +
++ For more details on the memory models and features, see the + atomic wiki. +
+
+typedef int v4si __attribute__ ((vector_size (16)));
+v4si res, a = {1,2,3,4};
+int x;
+
+res = 2 + a; /* means {2,2,2,2} + a */
+res = a - x; /* means a - {x,x,x,x} */
+
+ -std=c11 and -std=gnu11, in
+ addition to the previous -std=c1x
+ and -std=gnu1x.
+ -std=gnu11, now supported
+ with -std=c11), and the predefined
+ macros __STDC_UTF_16__
+ and __STDC_UTF_32__._Noreturn
+ and <stdnoreturn.h>)._Alignas, _Alignof,
+ max_align_t, <stdalign.h>).__builtin_complex is
+ provided to support C library implementation of
+ the CMPLX family of macros.-std=c++11,
+ -std=gnu++11, and -Wc++11-compat options,
+ which are equivalent to -std=c++0x,
+ -std=gnu++0x, and -Wc++0x-compat,
+ respectively.
+template<class W>
+class Q
+{
+ static const int I = 2;
+public:
+ friend W;
+};
+
+struct B
+{
+ int ar[Q<B>::I];
+};
+struct B {
+ virtual void f() const final;
+ virtual void f(int);
+};
+
+struct D : B {
+ void f() const; // error: D::f attempts to override final B::f
+ void f(long) override; // error: doesn't override anything
+ void f(int) override; // ok
+};
+
+struct E final { };
+struct F: E { }; // error: deriving from final class
+struct A {
+ int i = 42;
+} a; // initializes a.i to 42
+// Not actually a good approximation. :)
+constexpr long double operator"" _degrees (long double d) { return d * 0.0175; }
+long double pi = 180.0_degrees;+template <class T> using Ptr = T*; +Ptr<int> ip; // decltype(ip) is int*
+struct A {
+ A(int);
+ A(): A(42) { } // delegate to the A(int) constructor
+};
+class POD {
+ int a;
+ int b;
+};
+std::atomic<POD> my_atomic_POD;
+__cplusplus to the
+ correct value, 199711L for C++98/03,
+ and 201103L for C++11.
+ -fpermissive compiler flag will
+ allow the code to compile with a warning.
+
+
+template <class T>
+void f() { g(T()); } // error, g(int) not found by argument-dependent lookup
+void g(int) { } // fix by moving this declaration before the declaration of f
+
+template <class T>
+struct A: T {
+ // error, B::g(B) not found by argument-dependent lookup
+ void f() { g(T()); } // fix by using this->g or A::g
+};
+
+struct B { void g(B); };
+
+int main()
+{
+ f<int>();
+ A<B>().f();
+}
+const int &f(const int &i) { return i; }
+....
+const int &x = f(1);
+const int &y = f(2);x refers to the temporary allocated to hold the
+1 argument, which only lives until the end of the
+initialization; it immediately becomes a dangling reference. So the
+next statement re-uses the stack slot to hold the 2
+argument, and users of x get that value instead.
+
+Note that this should not cause any change of behavior for temporaries +of types with non-trivial destructors, as they are already destroyed at end +of full-expression; the change is that now the storage is released as +well.
-Wdelete-non-virtual-dtor
+ has been added to warn when delete is used to destroy
+ an instance of a class which has virtual functions and non-virtual
+ destructor. It is unsafe to delete an instance of a derived class
+ through a pointer to a base class if the base class does not have a
+ virtual destructor. This warning is enabled by -Wall.
+ -Wzero-as-null-pointer-constant
+ has been added to warn when a literal '0' is used as null pointer
+ constant. It can be useful to facilitate the conversion to
+ nullptr in C++11.
+ noexcept in most of the library;pointer_traits, allocator_traits
+ and scoped_allocator_adaptor; tuple; vector meets the allocator-aware container requirements; monotonic_clock with steady_clock; --enable-clocale=newlib configure option. <unistd.h>.-fstack-arrays has been added, which causes
+ all local arrays to be put on stack memory. For some
+ programs this will improve the performance significantly. If your
+ program uses very large local arrays, it is possible that you will
+ have to extend your runtime limits for stack memory.-Ofast flag now also implies -fno-protect-parens and -fstack-arrays.-ffrontend-optimize option and deselected by
+ the -fno-frontend-optimize option.-Wfunction-elimination warns about that.-faggressive-function-elimination option
+ allows the removal of duplicate function calls even for impure
+ functions.-Wreal-q-constant has been added, which
+ warns if floating-point literals have been specified using
+ q (such as 1.0q0); the q
+ marker is now supported as a vendor extension to denote quad precision
+ (REAL(16) or, if not available, REAL(10)).
+ Consider using a kind parameter (such as in 1.0_qp)
+ instead, which can be obtained via SELECTED_REAL_KIND.GFORTRAN_USE_STDERR environment variable has
+ been removed. GNU Fortran now always prints error messages to
+ standard error. If you wish to redirect standard error, please
+ consult the manual for your OS, shell, batch environment etc.
+ as appropriate.-fdump-core option and
+ GFORTRAN_ERROR_DUMPCORE environment variable have
+ been removed. When encountering a serious error, gfortran will
+ now always abort the program. Whether a core dump is generated
+ depends on the user environment settings; see the ulimit -c
+ setting for POSIX shells, limit coredumpsize for C shells,
+ and the WER user-mode dumps settings on Windows.-fbacktrace option is now enabled by default.
+ When encountering a fatal error, gfortran will attempt to
+ print a backtrace to standard error before aborting. It can be
+ disabled with -fno-backtrace. Note: On POSIX targets
+ with the addr2line utility from GNU binutils, GNU
+ Fortran can print a backtrace with function name, file name,
+ line number information in addition to the addresses; otherwise
+ only the addresses are printed.class) arrays are now supported.DO CONCURRENT construct has been
+ added, which allows the user to specify that individual loop
+ iterations have no interdependencies.-std=f2008ts permits programs that are expected
+ to conform to the Fortran 2008 standard and the draft Technical
+ Specification (TS) 29113 on Further Interoperability of Fortran
+ with C.OPTIONAL attribute is now allowed
+ for dummy arguments of BIND(C) procedures.RANK intrinsic has been added.ASYNCHRONOUS attribute
+ in GCC is compatible with the candidate draft of TS 29113
+ (since GCC 4.6).-mcpu=cortex-a7.-mvectorize-with-neon-double was added to
+ allow users to change the vector size to 64 bits.__flash, __flash1, …,
+ __flash5 and __memx has been added.
+ These address spaces locate read-only data in
+ flash memory and allow reading from flash memory by means of ordinary
+ C code, i.e. without the need of (inline) assembler code:
+
+const __flash int values[] = { 42, 31 };
+
+int add_values (const __flash int *p, int i)
+{
+ return values[i] + *p;
+}--with-avrlibc=yes in order to arrange for better
+ integration of AVR-Libc.
+ This configure option is supported in avr-gcc 4.7.2 and newer and will
+ only take effect in non-RTEMS configurations. If avr-gcc is configured
+ for RTEMS, the option will be ignored which is the same as
+ specifying --with-avrlibc=no.
+ See PR54461 for more technical
+ details.__int24 and __uint24.-maccumulate-args,
+ -mbranch-cost=cost and -mstrict-X
+ were added to allow better fine-tuning of code optimization.-fdata-sections now also takes affect
+ on the section names of variables with the progmem
+ attribute.%i to print a RAM address as I/O
+ address has been added:
+
+#include <avr/io.h> /* Port Definitions from AVR-LibC */
+
+void set_portb (uint8_t value)
+{
+ asm volatile ("out %0, %i1" :: "r" (value), "n" (&PORTB) : "memory");
+}%i modifier so that the
+ address is suitable to be used as operand in an I/O command.
+ The address must be a constant integer known at compile time."R" to represent integers
+ in the range −6 … 5 has been removed
+ without replacement.__builtin_ffs*, __builtin_clz*, etc.switch
+ instructionsEIND and indirect jumps on devices with
+ more than 128 KiB of program memory.RAMPD, RAMPX,
+ RAMPY and RAMPZ special function registers.OS_main and OS_task.-mavx2.-mbmi2.__builtin_clz*
+ using the lzcnt instruction is available via -mlzcnt.-mfma.-mfsgsbase command-line option is available that makes GCC
+ generate new segment register read/write instructions through dedicated built-ins.rdrnd instruction is available via -mrdrnd.-mf16c.-march=core-avx-i.-march=core-avx2.-march=bdver2 and -mtune=bdver2 options.-mx32 option.-mms-bitfields option
+ by default.__thiscall calling
+ convention for C++ class-member functions.--with-threads=posix
+ for Windows mingw targets.-march=octeon+ and -march=octeon2
+ respectively. Both options require GNU binutils 2.22 or later.-mfix-24k.
+ These workarounds require GNU binutils 2.20 or later.mips-linux-gnu
+ can now build n32 and n64 multilibs. The result is effectively
+ a 64-bit GNU/Linux toolchain that generates 32-bit code by default.
+ Use the configure-time option --enable-targets=all
+ to select these extra multilibs.-fno-delayed-branch now also stops the
+ assembler from automatically filling delay slots.-mno-pointers-to-nested-functions was
+ added to allow AIX 32-bit/64-bit and GNU/Linux 64-bit PowerPC users to
+ specify that the compiler should not load up the chain register
+ (r11) before calling a function through a pointer.
+ If you use this option, you cannot call nested functions through a
+ pointer, or call other languages that might use the static chain.msave-toc-indirect was added to allow AIX
+ 32-bit/64-bit and GNU/Linux 64-bit PowerPC users control whether we
+ save the TOC in the prologue for indirect calls or generate the save
+ inline. This can speed up some programs that call through a function
+ pointer a lot, but it can slow down other functions that only call
+ through a function pointer in exceptional cases.#pragma GCC target or
+ __attribute__ ((__target__ ("target")))
+ code sequences. In addition, the target macros are updated.
+ However, due to the way the -save-temps switch is
+ implemented, you won't see the effect of these additional macros
+ being defined in preprocessor output.-msoft-atomic has been added. When it is
+ specified, GCC will generate GNU/Linux-compatible gUSA atomic sequences
+ for the new __atomic routines.-ml with -m2a* will now result in a compiler
+ error.-mbranch-cost option has been fixed.tst #imm,R0 instruction.-mflat has been reinstated. When it is
+ specified, the compiler will generate code for a single register
+ window model. This is essentially a new implementation and the
+ corresponding debugger support has been added to GDB 7.4.-mtune=native and
+ -mcpu=native has been added on selected native platforms
+ (GNU/Linux and Solaris).visintrin.h has been added.alignaddr is now
+ supported.const, which
+ should increase the compiler's ability to optimize VIS
+ operations.%gsr register
+ and how it behaves as an input for various VIS instructions.fzero, the compiler can now generate
+ fone instructions in order to set all of the bits
+ of a floating-point register to 1.bmask,
+ bshuffle, and non-condition-code
+ setting edge instructions have been added. Their availability
+ is controlled by the new -mvis2 and
+ -mno-vis2 options. They are enabled by default
+ on UltraSPARC-III and later CPUs.-grecord-gcc-switches) was added that
+ appends compiler command-line options that might affect code
+ generation to the DW_AT_producer attribute string in the
+ DWARF debugging information.
+ -gstrict-dwarf command-line option.
+ This is the list +of problem reports (PRs) from GCC's bug tracking system that are +known to be fixed in the 4.7.1 release. This list might not be +complete (that is, it is possible that some PRs that have been fixed +are not listed here).
+ +The Go frontend in the 4.7.1 release fully supports +the Go 1 language +standard.
+ +This is the list +of problem reports (PRs) from GCC's bug tracking system that are +known to be fixed in the 4.7.2 release. This list might not be +complete (that is, it is possible that some PRs that have been fixed +are not listed here).
+ + + + + + +Copyright (C) +Free Software Foundation, Inc. +Verbatim copying and distribution of this entire article is +permitted in any medium, provided this notice is preserved.
+ +These pages are +maintained by the GCC team. +Last modified 2012-09-20.
+ +